Watch Dog, as the name suggests, is an app that lets your gear2 watch over your phone in a situation where you are not in the vicinity of your phone but need to keep an eye on it.
For example, you are in a bar and have gone to the loo and realize that your phone is on the bar table, you can then activate Watch Dog and at that moment if the phone is picked you get a notification on your gear 2 with an option to alert or ignore. So if you know who is picking your phone, you ignore, else you alert and an alarm, with full volume regardless of your phone volume, will go off. Additionally, the phone will also take a picture using the front camera and send it to your gear 2 for you to see who is handling your phone.
The alarm can be muted through the gear2 if the person is someone you know.
So you don't have to rely on your weak memory anymore, because now there is Watch Dog!!!